60 BULLETIN 1369, U. $§. DEPARTMENT OF AGRICULTURE 
surface, where they could be seen distinctly. Not only the time of 
molting was observed in this way but the changes in color of the 
last stage could be observed and the approach of complete develop- — 
ment noted and emergence watched for. 
In order to eliminate any possible adverse effect on the develop- — 
ment of the larve by these repeated observations, the appearance im 
> 
the subdermal tissues of several hundred third-stage larve was deter- 
mined by the method indicated, following which they were not dis- 
turbed except to make occasional notes on their presence until about 
the date of emergence from the host. The average time for the 
development in the case of those larve examined for molts, ete., 
was practically the same, however, as in the case of those which 
were not disturbed. 
As a method of checking up on the observations on the various 
larvee it was found best to make a rough diagram of the backs of the 
hosts, indicating the position of each larva and assigning it a num- 
ber. In order to facilitate the location of each larva the position 
on the animal’s back was indicated by clipping the hair. In the 
early observations the hair was clipped close to the skin immediately 
over the warble hole. Later, as it was thought that the development 
might be interfered with by exposure, clips were made in the hair 
of the host just above or below the position of the warble. 
The minimum period of development of larve of H. lineatum in 
the backs of cattle at Dallas, Tex., based on about 200 records, was 
between 35 and 47 days. Another period noted was 38 to 40 days, 
4 
and still another 39 to 46 days. In several other cases the period © 
ranged between 39 and 50 days. The maximum period was between 
78 and 89 days. The average total developmental period, based on 
104 warbles examined at frequent intervals, was 56.3 days. A few 
representative records of the development in the backs of cattle are 
given in Table 7. 
The average period of development of 222 other larve of HZ. 
lineatum in which the date of appearance under the hide and the 
date of emergence from the host were determined without disturb- 
ing the larve by making observations on molts was 57.74 days. 
At Uvalde, Tex., D. C. Parman recorded the duration of the 
larval period in the backs of cattle for larve of H. lineatum. The 
minimum period noted was 43 to 45 days, the maximum 54 days, 
and the average 49.4 days. 
Six accurate records of the period of development of H. bovis 
in the backs of cows were made in New York. The maximum was 
77 days, the minimum 65 days, and the average 72.8 days. 
Apparently the duration of development in the backs of cattle 
is not influenced by individual, breed, or age of the host. The 
writers’ records indicate that the development may be slightly 
‘shorter at Uvalde, Tex.. than at Dallas, and that the time spent in 
the subdermal tissues of cattle averages slightly longer in the case 
of larve coming up to the backs in the early part of the season. 
For example, the average period of those which appeared in the 
subdermal tissue in October and early November was about 58 
days, whereas in those which appeared during the latter part of — 
December and in January it was about 51 days. 
